Water quality and pesticide contamination in agricultural streams: assessing white-rot fungi and biochar treatments as remediation strategies

Pesticides used in agriculture, such as herbicides and fungicides, can reach water bodies through runoff and are a threat to freshwater ecosystems. Traditional methods to remove organic pesticides often lack efficiency or are too costly at scale. White-rot fungi (WRF) offer a green alternative by producing enzymes that break down persistent pollutants like pesticides. Biochar, made from organic waste, is another sustainable option due to its high adsorption capacity and carbon sequestration potential. This study evaluates water quality and pesticide contamination in five agricultural streams in Norway, and tests treatments with WRF and biochar as cost-effective, eco-friendly solutions for removing pesticides from surface waters. Eutrophication status based on total phosphorous ranged from high to bad conditions, while total nitrogen was relatively high at all locations. 35 pesticides were detected in at least one location, with concentrations ranging from 0.001 μg/l to 9.1 μg/l (for fluroxypyr). The most frequently detected compound was trifloxystrobin acid (present in all studied locations). Three water treatments were tested in the laboratory, two using WRF, in the form of spent mushroom substrate (SMS) and pellets, and one using biochar. The approaches showed promise in reducing pesticide concentrations, with biochar (average removal efficiency of 94 %) significantly outperforming WRF-based treatments (27 % average removal efficiency for WRF: SMS and 20 % for WRF: pellets). However, all treatments led to increases in total phosphorus, though the increase was lower for WRF: pellets. WRF treatments also significantly increased total organic carbon and total nitrogen, which raises concerns about the risk of eutrophication.